Field of the Invention
The present invention relates to a toner for use in an electrophotographic method, an electrostatic recording method, a magnetic recording method and the like.
Description of the Related Art
At present, one component development method using a magnetic toner is widely employed in a copying machine and a laser beam printer, due to cost advantage and simple configuration of devices.
The magnetic toner is usually manufactured by a pulverization method, having an average circularity of 0.960 or less and a toner surface with irregularities in many cases.
At present, various investigations on both of the toner and the main unit are under way for further prolonged life of a copying machine and a printer which use the magnetic toner.
Examples of the effects of expected prolonged life in an electrophotographic system configuration on a toner include a prolonged agitation time for the toner in a toner container due to prolonged life. Accordingly, the physical load on the toner increases.
The increase in physical load on a toner in a process accelerates the embedding of small particle-diameter external additives existing on the toner surface into the toner surface, resulting in the occurrence of phenomena such as reduction in the flowability of toner, degradation in charging characteristics, and increase in physical adhesion. Eventually, image defects, density reduction and the like may be caused in some cases.
Conventional small particle-diameter external additives have not sufficiently solved the problems. The reason is that the governing factor of embedding of external additives into the toner surface is the particle diameter of the additives. As a logical sequence, the smaller the particle diameter is, the more easily the additives are embedded.
Accordingly, many attempts to use larger particle-diameter external additives as spacer particles have been conventionally made in dealing with the prolonged life.
Since large particle-diameter external additives have a large contact area with the toner surface, the impulse to the toner per unit surface area can be reduced. Consequently, embedding into the toner surface can be suppressed compared to small particle-diameter external additives.
For example, in Japanese Patent Application Laid-Open No. 2005-3726, large particle-diameter silica particles are added as external additives with expectation of suppression of embedding and prolongation of the life to a certain extent. In Japanese Patent Application Laid-Open No. 2005-202131, composite particles of small particle-diameter silica and large particle-diameter melamine resin particles are used as external additives.
However, the addition of large particle-diameter external additives to toner particles having a surface with irregularities may cause the large particle-diameter external additives to be swept to the concaves on the surface of a toner particle, resulting in an uneven distribution as shown in FIG. 1A.
The uneven distribution of the large particle-diameter external additives swept to the concaves on the surface of a toner particle may cause difficulty in achieving a prolonged life in some cases, though added for prolongation of life, since they cannot perform their inherent function as the large particle-diameter external additives as spacer particles. The reduction in adhesion to the toner surface due to the enlargement of particle diameter easily allows for detachment from the toner, causing a further problem that components are markedly contaminated therewith during long-term use.
In dealing with the problems, for example, International Publication No. WO 2013/063291 discloses an example of using an organic-inorganic composite fine particle as a spacer particle including inorganic fine particles fixed to the surface of an organic fine particle.
Since the organic-inorganic composite fine particle has convexes derived from the inorganic fine particles on the surface, the convexes as wedge is driven into the toner surface. Consequently, the organic-inorganic composite fine particles are hardly swept to the concaves on the surface of a toner particle to form an uneven distribution as shown in FIG. 1B, as compared to conventional spherical large particle-diameter external additives.
As a result of investigation by the present inventor, however, the effectiveness in not necessarily achieved, depending on the type of magnetic material of toner particles. In some cases, the organic-inorganic composite fine particles are swept to the concaves on the surface of a toner particle to form an uneven distribution as similar to conventional large particle-diameter external additives.
As described above, although the addition of large particle-diameter external additives is effective for achieving a prolonged life, there exist many negative effects which require further countermeasures.